1. Field of the Invention
The invention relates to a measuring device for measuring the hitting parameters of a golf club, including a measuring device with at least one horizontally pointing reflective light barrier, a data acquisition device integrated into the measuring device, reflectors with retro-reflective surfaces attached to the golf club in corresponding relationship with the reflective light barriers and an evaluating-, display- and storage unit to which the data acquisition device forwards the acquired data. The invention further includes a calibration device for measuring the translational and angular deviations relating to the measuring device according to the invention.
2. The Prior Art
A generally known sentence goes: “The way the ball is hit determines the way it flies (or rolls)”. In the “PGA Teaching Manual, Lehr-und Lernunterlagen fur Auszubildende zum Diplom-Golfprofessional”, issued 2001 by the Professional Golf-ers Association of Germany e.V. PGA Aus-und Fortbildungsgesellschaft mbH, PGA-Professional Oliver Heuler writes in his article “Golftechnik” that at the hitting moment eight parameters determine how the golf ball will fly, no matter, how these parameters are brought about. These hitting parameters are                1. Club face position        2. Dynamic lie        3. Dynamic loft        4. Horizontal angle of approach (swing path)        5. Vertical angle of approach        6. Hit the sweet spot (horizontally)        7. Hit the sweet spot (vertically)        8. Club head speed.        
Much effort has been made to determine these hitting parameters and to use them for teaching purposes. In U.S. Pat. No. 4,304,406 it is disclosed to measure the hitting parameters    1. club face position angle open/closed (Aoc),    2. horizontal angle of approach in/out (Aio),    3. sweet spot position (SSP) and    4. club head speed (V)    by photo- or infrared detectors. A plurality of such detectors is integrated in a defined pattern into a playing mat and be illuminated from an intensive (infrared-) light source above the tee.
The detectors measure the relative times of shadowing during the passage of the club head. Aoc, Aio, SSP, and the club head speed V can be calculated from the known geometry of the detector pattern, the position of the light source and the times of shadowing.
In principle, this is a robust measurement method, but it is a disadvantage that the (infrared-) light source constitutes an annoyance in the view field of the player. Further, the detectors in the playing surface are prone to contamination and/or to damaging by the club head. A further disadvantage is the requirement of a special golf mat for the measurements.
Another method to determine the hitting parameters Aoc, Aio, SSP and V is known from U.S. Pat. No. 4,254,956. Especially arranged optical sensors in a playing mat are at this applied likewise. However, this method does not solely use clearly defined times of beam interruption, but the natural ambient light and analog signals that represent the degree of shadowing effects on particular diffusor disks during the passage of the club head. Thereby the analysis becomes difficult and is particularly problematic where the ambient light intensity varies quickly. Contrary to all appearances, this is always the case where people exercise in the light of fluorescent lamps with classical ballasts.
U.S. Pat. No. 4,306,722 discloses a method to determine the hitting parameter Aoc with high accuracy. It employs a kind of reflective light barrier. Depending on Aoc a mirror at the club head determines the point where the light barrier beam hits a two-dimensionally extended detector. This point is detected by an analogously operating electronic system and is converted to a Aoc display value. With this method very precise results may be achieved, but in practice it shows some severe disadvantages:    1. A mirror has to be arranged and exactly aligned between the player and the tee.    2. Another exactly aligned mirror must be attached to the club head which may be damaged in cases of imprecise ball contact.
The above mentioned patents have in common that their realization depends on a large number of detectors or on a precise, under practical circumstances barely realizable beamline. These and similar measurement arrangements, in particular with optical sensors which are specifically arranged in a golf mat, which operate with ambient light or work as reflex sensors, are available on the market today.
In CA 2 367 797 another method for measuring the hitting parameters Aoc, Aio, SSP and V and in addition the initial ball speed and the rotation of the ball (sidespin and backspin) is described. According to this method spots of highly reflective foil are glued on the club head. Two electronic cameras and a flashlight record the critical stage of the golf swing. A light barrier provides the timing of the exposure and triggering of the flash light. The golf ball used is marked with special color rings. During the golf swing the flash lights are actuated several times, so that the cameras yield multiple exposure (stereo-) images in which the computer searches the reflective spots from which it calculates the club position at the instance of the exposure. The same computer determines the trajectory and rotation of the golf ball from the views of the golf ball and from the color rings on it.
This method provides information about the kinetics of the club, but it has also severe disadvantages. The assembly is so bulky, that practice may just be possible in fixed cabins. Furthermore, the arrangement of one branch of the triggering light barrier between the player and the tee is needed. Further, the costs for the components should prevent a wide-spread use.
U.S. Pat. No. 6,095,928 discloses a three-dimensional swing analysis in which the object moves through a space that is defined by a three-dimensional coordinate system. Measured are the angles, at which the object or the club head, respectively, pass through this space. Infrared LEDs produce diverging cones of light that shine on ball-shaped or spherical reflectors attached to the club head or to the shaft above the club head, whereupon the angles of reflection are determined by sensors, e.g. by photodiodes (InGaAs-Avalanche Photodiodes IADs). The system displays the trajectory of the club head. The hitting parameters are not determined in this way, the measurement setup is not qualified for that purpose. A further disadvantage is the liability of the measurement to faults by the use of ball-shaped reflectors which necessitate the use of special filters.
The WO 98/18010 also discloses a golf swing analyzer that measures the pre- and post-impact position and/or the movement of the golf club head and/or of the golf ball (spin components) during a golf swing. The measuring instrument comprises one or several light sources or one or several means that react to the reflections by a moving object (slotted openings and/or cylindric lenses arranged in a de-fined plane) that give a signal if the moving object interrupts a defined plane of detection. The moving object may be a golf club to the club head of which a lamellar or circular reflective zone or LEDs are attached. The setup is not suited to determine the hitting parameters. The same holds for US 2005/0130755 A1.
DE 101 03 449 A1 discloses a mobile setup for measuring the speed and/or the speed profile of a golf club head with the measurement being possible with or without golf ball. Therefore a sensor unit is attached to the golf club head and a display unit is attached to the golf club shaft and between them a flexible wire or a wire-less connection is foreseen for transferring data between the sensor unit (10) and the display unit. The gauging is based on determining the relative air speed with a Pitot tube or Prandtl's Pitot tube or based on the negative pressure or suction by means of a venturi meter or electronically (measurement of the movement of the golf club head relative to the ambient medium or relative to the ambient material, respectively) with a small lightweight sensor attachable to the golf club head without external transmitter- and receiver unit, or by radar (Doppler shift) or by choke measurement. In case of measurements with radar, a reflector is mounted on the shaft side of the club head. Alternatively or complementing the reflector, the golf ball-sided face of the club head can also be used as reflecting area.
Since the radar transceiver is arranged behind the golf ball in the heading direction of the ball flight, there is always some risk that badly struck golf balls may hit and damage the radar unit after takeoff. Hitting parameters cannot be assessed with such a simple measuring equipment. Displaying the maximum speed does not tell anything about the speed at the very moment of the impact, since the maximal club head speed may have been achieved shortly before or behind the point of ball contact.
DE 101 19 740 A1 discloses a putting trainer. In order to control the orientation of the putter club blade (Aoc), a narrow collimated beam of light is directed from an emitter to a reflector at the putter and to a receiver. The receiver is equipped with a row of particularly narrowly arranged sensors (photo transistors) on both sides of a central sensor. The reflector is a plane mirror whose back side butts against the club face. The emitter contains a laser whose narrow beam is detected after reflection by the mirror by the adjoining detectors in the receiver. A switching device (light barrier/photo transistor), which gives a signal when the put swing passes the golf ball position, activates the trainer for a short while. The golfer is shown minimal deviations of his putter from the ideal target line and furthermore deviations from the hitting point by light emitting diodes which are associated to each sensor in the receiver. This means that it is indicated whether the sweet spot (SSP) has been hit or missed. In this case the central sensor and the target position lie on top of each other. However, putting with a golf ball is precluded during this kind of training, else the mirror would be damaged. Although an embodiment is mentioned, in which the mirror is offset laterally to allow for putting a golf ball, such a setup is not suited for full swings, be it with or without ball.
US 2003/0054898 A1 discloses a golf swing analyzing system. In the surface of the casing body, which is made of a non-metallic material, a tee and optical sensors, preferably infrared reflective light barriers are inserted in three rows that run perpendicularly to the swing line left and right from the tee. Further sensors may be arranged centered in relation to the tee in towers at the front sides of the casing body to allow for measuring the height of the swing path. The sensors emit narrow infrared beams. A reflective strip is placed on the bottom side of the club head. By this strip the infrared beams are reflected during the passage of the club head. The sensors generate electrical signals which are transmitted via conventional cables to a data acquisition unit (controller) and converted in digital signals. From there the signals are forwarded to a evaluating-, display- and storage unit (computer) that calculates the hitting parameters Aoc, Aio, SSP and V from the temporal pattern of the signals. Displayed are both the actual data and comparative historical swing information.
This golf swing analysis system operates with numerous infrared reflective light barriers (37 pairs of QED123/QS-D123), each having a low angular resolution. The aperture angle of the transmitters is ±9°, the one of the receivers ±12°. The great number of infrared reflective light barriers makes the proposed system expensive. Further, the current needed alone for the infrared emitters sums up to significantly more than 3 A, which impedes battery-based operation. However some of the sensors serve the only purpose to trigger the system and to activate the current feed to the subsequent sensors. The essential components are integrated into a special golf mat, made of an elastic material. Such a setup is damageable by too lowly accomplished swings, particularly because the position and adjustment of all light barriers is essential for their aforementioned function. Too lowly accomplished swings also quickly disable the reflective strips glued to the bottom side of the club head so that these strips must be regarded as consumable material. A good temporal resolution of the proposed design can only be expected if the club head passes the mat at low distance. Else the aperture angle of the sensors is likely to produce strong time-jitter of the output signals, which renders the measurement imprecise or useless. (Already at 5 cm distance the acquisition cone has a diameter of 1.5 cm.) The necessarily short working distance causes another problem. Dependant on the type and brand, golf club heads have highly varying outer contours, often with reflective, almost mirroring surfaces. Hence the infrared reflective light barriers must be expected not only to respond to reflections from the retroreflective strip, but also to reflections from other spots on the club head surface.
US 2005/0202907 A1 describes an extension of US 2003/0054898 A1. It discloses some technical details that allow for an estimate of the achievable fidelity. The patent file mentions several times the temporal resolution of the sensors to be 10 μs ( 1/100000 s). In this time the golf club head moves forward approx. 0.278 mm at a speed of 100 km/h (which corresponds to a drive swing of moderate speed). The open/close-angle is determined by two sensors which can have a distance of maximally 5 cm on a line perpendicular to the moving direction of the club head to be safely flown over as a pair. Hence the angular resolution is at best
      arcsin    ⁡          (                        0.27          ⁢                                          ⁢          mm                          50          ⁢                                          ⁢          mm                    )        =      0.31    ⁢    °  
According to US 2005/0202907 A1 the height is determined by up to 4 displacement sensors that work by the triangulation principle of measurement. In comparison to other industrial applications, these sensors must respond relative quickly (at only 100 km/h and at a depth of 15 mm, which is absolutely usual for irons, the underside lingers 0.54 ms over the sensor). This necessitates expensive special designs (standard sensor approx. 1000 ), which in addition are exposed to the risk of damage by the club head.
From WO 99/49944 a measuring setup is known, in which hitting parameters are determined by four laser sensors which are attached to the club. The sensors pass one or more fan-shaped laser beams which originate from one or more laser sources between the feet of the player. The responses of the laser sensors are transmitted via a short distance radio link to the evaluation electronics. Resolutions are reported to be 0.3° for the open/close angle, 0.1° for the dynamic loft, and 0.1°for the dynamic lie. The sweet spot resolution of the prototype is indicated to be 5 mm.
A disadvantageous feature of this setup is the position of the laser source near the feet of the player, which constitutes a dangerous stumbling block. Further, the applied, vertically pointing laser fans are either severely restricted in their power density or they can lead to irritation or even damage to the eyes in the vicinity of the orifice of the laser source.
WO 2004/067099 A2 describes a golf swing analysis by a budget-priced video camera. Spheres of approx. 10 cm ø with distinctive high-contrast patterns are attached to the golf cub shaft directly below the grip zone. Alternatively, the spheres contain active light sources for practicing in low light conditions. That way the track of the club in the swing plane and particularly the posture of the player in the different stages of the swing movement can be reconstructed to correct the player. No indications are released concerning the achievable accuracy of hitting parameters like sweet spot or open/closed angle. A USB-camera serves as sensor. USB cameras are inexpensive, indeed, but they offer bad frame rates (consumer type USB-cameras today 80 fps at maximum) and cannot be synchronized to the stages of the swing.
Another analyzer with two cameras is known from U.S. Pat. No. 5,803,823. The analyzer monitors the movement of a golf club shortly before and during contact to the golf ball and the characteristics of the movement of the golf club shortly before contact to the golf ball. Both camera units take 2-dimensional images. At the golf club and at the golf ball, respectively two or more dot-shaped areas of retro-reflective material are arranged in a way that two flashes that are elicited in a flashlight get reflected by the dot-shaped areas and recorded by the camera units which are arranged opposite to the golfer as 2-dimensional patterns while the shutters are open. From the dot-patterns the trajectory of the club head and its orientation relative to the golf ball are determined whereas the characteristics of the movement of the golf club are determined by comparison of two positions of the illuminatable areas at the golf club in relation to the illuminatable areas at the golf club. Such an image analysis is extensive, expensive and coarsely rasterized. Another disadvantage of this kind of analyzer is that reflective dots have to be attached to the golf ball, which might get damaged at each stroke. Further, it is not possible to play without a golf ball with such a measuring setup.
Furthermore, in U.S. Pat. No. 5,803,823 two calibration setups for the measurement setup are described. The first calibration setup consists of a 3-dimensional models with 20 spots of ¼″ diameter for calibrating the two cameras. For localizing the sweet spot the second calibration setup provides to the measurement setup the information where the geometrical center is situated on the club face of the club head. Therefore a circular disk with three studs which are arranged in one X-axis and which point perpendicularly away from the disk and which also bear a retroreflective spot, is glued on the club face and calibrated. With a calibration photograph eleven constants of each camera plus the X-, Y-, and the Z-axis are determined.